During the processing in container handling machines, in particular in rotary machines, for example in labeling or printing, containers, for example beverage bottles or the like, are usually retained in peripherally uniformly distributed clamping units on a carousel which is driven continuously or discontinuously. To adjust the rotational positions of the containers with respect to the circular path of the carousel, the containers are preferably placed onto rotary plates and pressed downwards by a centering support, for example a centering bell, in the mouth region or the closing region. On the one hand, one has to take care here that the clamping force is sufficiently high so that a correct position of the containers in the clamping units remains ensured despite laterally acting forces, for example centrifugal forces and/or pressing forces or the like caused by the processing. On the other hand, maximum values of the clamping force must be observed, depending on the mechanical stability of the containers, to avoid an undesired deformation and/or damage of the containers.
It is well-known that suited clamping forces can be generated by mechanical pressure springs. In particular in the processing of empty plastic bottles, an additional stabilization of the containers, in particular during labeling, by applying an overpressure inside the container has proven successful. To lift the centering supports during the supply/removal of the containers to/from the rotary machine to a suited position, stationary stroke curves along which the centering units are running are usually employed.
A disadvantage of the above prior art consists in that the clamping force of mechanical pressure springs is fixed. If different container types which differ, for example, by their material properties, wall thicknesses or sizes, are to be processed in the rotary machine, such predetermined clamping forces are not suited or only suited to a certain degree. The clamping units must be consequently modified which is elaborate. Another disadvantage consists in the vertical position of the centering supports depending on the current location of the respective clamping unit at a section of the stroke curve. Therefore, when the rotary machine is standing still, the centering units cannot be lifted/lowered for a certain measure.
Therefore, there is a demand for clamping units for containers at rotary machines in which at least one of the above disadvantages is eliminated or at least attenuated.